(1) Field of the Invention
The present invention relates to an internal combustion engine controller to be mounted on an automobile, motorcycle, agricultural machine, industrial machine, ship machine or the like to control an electromagnetic load for driving a fuel injection device with a battery voltage as it is or at a boosted level, and more particularly to an internal combustion engine controller having a function to diagnose any trouble in a communication circuit or an oscillator circuit.
(2) Description of the Related Art
Known internal combustion engine controllers of this kind include a type equipped with an injector that directly injects gasoline into cylinders for the purpose of enhancing fuel efficiency or power output. Such the injector consumes much more energy than the action to open the injector valve on account of the use of highly pressurized fuel. Latest such injectors are more susceptible to trouble with an electromagnetic load or driver circuit element as they tend to involve an increase in the electric current flowing to an electromagnetic load (inductance load). This entails the need for more elaborate trouble diagnosis and higher precision.
In view of this problem, an internal combustion engine controller that controls electromagnetic loads such as this injector is usually provided with a voltage booster for obtaining a higher voltage than the voltage direct from the power source battery, and the voltage raised by this booster is applied to electromagnetic loads to increase in a short period of time the amperage of electricity supplied to the electromagnetic loads.
More specifically, in the electric current waveform of a typical injector that directly injects fuel into cylinders, the current fed to electromagnetic loads is raised with a boost voltage to a predetermined peak current stop level in a short period of time during the peak current supply period in the early stage of electricity supply. Next, to open the valve of the injector, the current supplied to electromagnetic loads should be maintained with a voltage direct from the power source battery, which is lower than the boost voltage. To keep this current supply to electromagnetic loads at a prescribed amperage, a high side driver connected to the electromagnetic loads is switched with a dedicated high side driver drive signal. Further at the end of injection, the duration of the descent of the current supplied to electromagnetic loads is shortened and the current supply to the electromagnetic loads is intercepted to quicken the closing of the injector valve.
The following is a description of clock trouble in such an internal combustion engine controller. In an internal combustion engine controller, which requires high-precision clock input signals for use in its internal circuits, generates with an internal oscillator circuit (including a known oscillator) clock input signals for driving internal circuits. In particular, the logic circuits and driving circuits of internal circuits operate according to the fall or rise edge of clock input signals that is detected.
However, there is a risk of clock input trouble, that is the failure of clock input signals from such an internal oscillator circuit to be normally inputted on account of disconnection of wiring, battery voltage short or ground short of input signals, trouble with oscillator, faulty mounting of components arising from a solder ball problem or any like cause.
In the event of such a clock input trouble resulting in the fixation of the clock input signals in a high or low state, the output signals of the logic circuits and driving circuits of internal circuits will be fixed in the high or low state. As the outputs of driving circuits for electromagnetic loads and of voltage boosting driving circuits (DC/DC converter driving circuits) are also fixed in the high or low state under the impact of this trouble, a continuous flow of high currents to electromagnetic loads will occur. If, for instance, the outputs of driving circuits for electromagnetic loads are fixed in an active state, the electromagnetic loads may be placed in an open-valve state, inviting a state of indefinite continuation of fuel injection. Or if the outputs of voltage boosting driving circuits (DC/DC converter driving circuits) are fixed in an active state, the current will continue to flow to the driving circuits themselves, involving a risk of ignition of the internal combustion engine controller.
To address this problem, today there is extensive use of configurations equipped with a communication circuit as a logic circuit of internal circuits to provide a function to communicate (output) the findings of trouble diagnosis regarding electromagnetic loads to a microprocessor disposed in the internal combustion engine controller. Usually such a communication circuit gives outputs in a mutually connected serial interface. Some of the known internal combustion engine controllers have a trouble diagnosing function for external circuit groups including driving circuits. The trouble diagnosing function of an already developed product monitors signals generated by a trouble detection circuit in the internal combustion engine controller and transmits data on the findings of trouble diagnosis to a microprocessor by serial interface.
Note will be made hereupon of a product, as a typical known internal combustion engine controller, which is provided with a function to transmit at regular intervals of time information on any faulty channel and the state of the fault in external circuits to a microprocessor by using serial interface mutually connecting the microprocessor and a serial interface circuit. Where a large number of power switches are present, such a product transmits diagnostic findings by increasing the quantity of data to be sent by serial interface, but this involves the problem of increased software loads on the microprocessor. The reason for increasing the quantity of data to be sent by serial interface here is that, if the quantity of data to be sent were kept small, it would be impossible to transmit information on faulty ones among all the channels and the state of the fault in external circuits to the microprocessor as diagnostic findings, resulting in impossibility, when more than one fault have occurred at the same time in a trouble detecting device including power switches for controlling ignition and fuel injection, to send multiple sets of trouble diagnosis information to fully communicate the diagnostic findings.
In an attempt to solve this problem, internal combustion engine controllers capable of detecting even multiple troubles regarding electromagnetic loads (battery voltage short, ground short, short or open load) without increasing the quantity of data communicated have also been developed.
One example that can be cited here is an engine controller that has a serial interface circuit to transmit diagnostic findings to a microprocessor by serial interface, accomplishes the transmission of diagnostic findings in one round of communication with serial interface signals of a prescribed number of bits, provides the serial interface signals of the diagnostic finding output with a bit indicating the presence or absence of multiple troubles and determines whether or not there are multiple troubles (see Japanese Patent Application Laid-Open Publication No. 2003-074401).
This engine controller (internal combustion engine controller) accomplishes transmission of diagnostic findings in one round of communication with serial interface signals of a prescribed number of bits, permits determination of whether or not there are multiple troubles according to a bit indicating the presence or absence of multiple troubles provides in the serial interface signals of the diagnostic finding output and can thereby determine, without having to increase the quantity of data communicated, any multiple troubles that have occurred.
Other examples of related known art include a microprocessor-equipped device that can detect the stop of clocks supplied to the microprocessor with a simple circuit that can be made up of a small number of components and prevent serious trouble from arising (see Japanese Patent Application Laid-Open Publication No. H4-043436),